A 32-year-old patient is described who presented with severe cognitive deficits and major cortical and cerebellar atrophy. Investigations included numerous clinical laboratory tests, magnetic resonance imaging, [F-18]2-fluoro-2-deoxy-D-glucose positron emission tomography and detailed neuropsychological examinations. Tests covered mood, intelligence, attention and concentration, language, verbal fluency, various memory abilities, and cognitive flexibility. Furthermore, some experimental testing procedures were applied, such as drawing objects, and transcoding verbal and Arabic numerals. Laboratory findings failed to give any indication for viral, bacterial, genetic or metabolic diseases, or for chronic intoxication. In particular no presenilin genes were found. Neuroradiology revealed very severe cortical and less severe cerebellar degeneration. In most neuropsychological tests, the patient was greatly impaired. In spite of some inconsistencies at the anatomical and cognitive levels, it is concluded that, in spite of his young age, the patient suffered from an unusual form of Alzheimer's disease.